by a mycoplasmal organism (/3/5). Mycoplasmas are transmitted through root 
grafts, or by the whitebanded elm leafhopper (43) that is widely distributed in the 
Eastern United States. The leafhopper ingests the mycoplasma while feeding on the 
sap of a diseased tree. Later, the disease organism is transmitted when the insect 
feeds on a healthy tree. 
Courtesy G. N. Lanier, SUNY Coll. Environ. 
Sci. & For., photo by George Snyder 
Figure 3.—Elm twig with streaking symptomatic of Dutch 
elm disease. 
Foliar symptoms of elm phloem necrosis vary but are somewhat similar to those 
produced by drought, girdling, and certain other tree diseases. Symptoms may first 
appear on a single branch or a portion of the top, but most often the entire tree is 
symptomatic. In large trees, there 1s usually an apparent thinning of foliage in the 
top or at the outer tips of branches. This is followed by a general thinning of foliage 
throughout the crown. Generally, the leaves become chlorotic but some leaves 
become dry and brown. Defoliation and tree death occasionally happen within 3 to 
4 weeks but it usually requires from | to 1’ years. Before the tree dies, a typical 
yellow to butterscotch discoloration of the phloem develops (fig. 4). In large trees 
this discoloration is usually found only in large roots and the lower part of the trunk. 
In most small trees, and occasionally in large ones, it may be found in the upper 
part of the trunk and in branches. The butterscotch-colored phloem of American 
elm with elm necrosis has a faint odor of wintergreen, especially if the plant part is 
enclosed briefly in a bottle. 
During ephiphytotics such as occurred in the Central States in the late 1930’s and 
1940’s, elm phloem necrosis killed numerous valuable shade tree elms in many 
cities and towns (fig. 5). During the 1950’s the disease was at a low ebb, but more 
recently the disease is again on the increase in New York, Ohio, and Pennsylvania. 
Beech bark disease is a destructive disease of American and European beeches 
and all their varieties. It is caused by related fungi, Nectria coccinea var. faginata 
Lohman, Watson, & Ayres and N. galligena Bres. (250). These pathogens gain 
entry into the tree through tiny ruptures in the bark caused by the feeding of the 
beech scale. The scale and probably the fungus are of foreign origin. The disease, 
21 
